JPH0949483A - Plug with pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To small suppress hysteresis of rising/lowering of a pressure in a combustion chamber, while the pressure in the combustion chamber can be high accurately detected. SOLUTION: A main unit metal fitting 14 has an insertion cylinder 16 inserted into an insertion hole 6, and a thread is not formed in the periphery of this cylinder. As a means for fixing the main unit metal fitting 14 to a cylinder head 4, a cap nut 15 provided in a separate unit is used. This cap nut 15 is screwed into a recessed part 5 of the cylinder head 4, and a seat part 17 of the main unit metal fitting 14 is pressed to a bottom of the recessed part 5 through a gasket 19 and a pressure sensor 3. In the case of exploding a mixture in a combustion chamber 1, since exhaust gas is prevented from infiltrating as in prior art to a fine clearance of a screw fitting part, an in/out flow of gas in the screw fitting part is prevented from being caused, and hysteresis of the pressure sensor 3 is suppressed. Since pressure rising energy is prevented from being absorbed in the screw fitting part, detecting accuracy of the pressure sensor 3 is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plug provided with a pressure sensor for detecting the pressure inside a combustion chamber, and is particularly suitable for being applied to a spark plug.

[0002]

2. Description of the Related Art As a technique for detecting the pressure in a combustion chamber,
For example, it is known that a pressure sensor is attached to a spark plug screwed into a cylinder head of an engine. Here, a general spark plug without a pressure sensor has a structure in which a screw fitting part of a metal shell is screwed into an insertion hole of a cylinder head, and the screw fitting part is screwed into an insertion hole of a cylinder head. So, the seat of the metal shell is
The structure is such that it is pressed against the cylinder head via a gasket.

Therefore, as shown in FIG. 8, a conventional spark plug with a pressure sensor has a seat portion 102 of a metal shell 101.
(Corresponding to the pressing portion of the present invention) and the cylinder head 10
3, an annular pressure sensor 104 is arranged, and the screw fitting portion 105 of the metal shell 101 is screwed into the insertion hole of the cylinder head 103 to attach the pressure sensor 104. In this state, the pressure sensor 104 is in a state in which an axial force is applied by screwing the metal shell. Therefore, when a combustion pressure is generated in the combustion chamber, the spark plug receives the combustion pressure, the axial force applied to the pressure sensor 104 changes, and the pressure sensor 104 outputs a signal according to the change in the axial force.

[0004]

In the conventional structure, since the screw fitting portion 105 for fixing the plug to the engine is connected to the combustion chamber 106, when the combustion pressure is generated in the combustion chamber 106, a high pressure is generated. Of the combustion gas flows into the minute gap of the screw fitting portion 105, and the combustion gas flowing into the minute gap of the screw fitting portion 105 flows out due to the pressure drop in the combustion chamber 106. Especially when the pressure is lowered, the outflow of gas becomes gradual.
Thus, in the conventional structure, the screw fitting portion 105
Due to the inflow of gas into the minute gap and the gradual outflow of gas, there is a problem that a large hysteresis occurs in the detection value of the pressure sensor 104.

That is, in the conventional structure, when the pressure in the combustion chamber 106 is increased, the plug is pushed up to the outside of the combustion chamber 106, gas is introduced into the screw fitting portion 105, and when the pressure is reduced, the plug tries to return to its original position. Also, the screw fitting part 105
The gas that has flowed into will not be exhausted, and the return of the plug will be poor. As a result, the detected value of the pressure sensor 104 does not follow the actual change in the combustion pressure.

Further, in the conventional structure, the energy at the time of pressurization of the combustion chamber 106 is partially absorbed by the screw fitting portion 105 in the insertion hole before reaching the seat portion 102, so that the detection accuracy of the pressure sensor 104 is high. There was also a problem that the value decreased.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. An object of the present invention is to detect the pressure in the combustion chamber with high accuracy by a pressure sensor, and to increase or decrease the pressure in the combustion chamber. An object of the present invention is to provide a plug with a pressure sensor that can suppress hysteresis to a small level.

[0008]

The pressure sensor plug of the present invention employs the following technical means. [Means for Claim 1] A plug with a pressure sensor includes an insertion portion that is inserted into an insertion hole that communicates with a combustion chamber of an engine, and has a pressing portion that is pressed toward the engine, the engine and the plug. And a pressure sensor arranged between the pressing unit and the pressure unit. Then, the plug is provided so as to be screwed into the main body portion having the pressing portion and the engine, and is screwed into the engine,
The main body portion is fixed to the engine, and a tubular cap nut for pressing the pressure sensor between the pressing portion and the engine is provided.

[Means of Claim 2] In the plug with pressure sensor of Claim 1, the plug is a spark plug for igniting the inside of the combustion chamber, and a center electrode to which a high voltage is applied, and the center electrode is insulated and held. And an metal shell that is fixed to the engine while holding the insulator. The metal shell is formed with a screw to be screwed into the engine in a portion that is inserted into the insertion hole. By fixing this metal shell to the engine with the cap nut, the pressure sensor interposed between the metal shell, the insulator, the center electrode, and the seat of the metal shell is fixed to the engine. It is characterized by being done.

[Means for Claim 3] In the plug with a pressure sensor according to claim 2, the engine in which the insertion hole is formed has an annular step portion for reducing the inner diameter on the combustion chamber side in the insertion hole. And a ring-shaped step contact portion that contacts the step portion is formed in a portion of the metal shell that is inserted into the insertion hole.

[0011]

[Operation and effect of the invention]

[Operation and Effect of Claim 1] The pressure sensor plug is
As described above, the main body having the pressing portion for pressing the pressure sensor against the engine and the cap nut for fixing the main body to the engine are provided, and the main body is fixed to the engine by screwing the cap nut into the engine. In addition, a structure was adopted in which the pressure sensor is pressed between the pressing part and the engine.

Therefore, when the combustion pressure is generated in the combustion chamber, the high pressure combustion gas does not flow into the minute gap of the screw fitting portion as in the conventional case. In other words, like the conventional technology,
The pressure sensor can receive the pressure change in the combustion chamber without the pressure sensor being affected by the inflow of the combustion gas into the minute clearance of the screw fitting portion and the effect of the gradual outflow of the combustion gas from the minute clearance. As a result, the hysteresis of the pressure sensor due to the pressure change in the combustion chamber can be suppressed smaller than in the conventional case.

Further, in the prior art, when the combustion pressure is generated in the combustion chamber, the energy at the time of pressurization of the combustion chamber is partially absorbed by the screw fitting portion in the insertion hole before reaching the pressing portion. However, in the present invention, the boosting energy is not directly absorbed in the insertion hole and is directly transmitted to the pressing portion. As a result, the output of the pressure sensor is increased and the detection accuracy in the combustion chamber can be improved as compared with the conventional case.

[Operation and Effect of Claim 2] Even when the plug of the present invention is applied to a spark plug, the same operation and effect as in Claim 1 can be obtained.

[Operation and effect of claim 3] When the plug of the present invention is applied to a spark plug, since there is no screw fitting portion in the insertion hole as in the prior art, the contact area between the metal shell and the engine It is feared that the heat dissipation of the spark plug will deteriorate due to a decrease in
By abutting the step portion formed in the insertion hole of the engine and the step contact portion formed on the metal shell, the contact area between the metal shell and the engine is increased, and heat is transferred from the metal shell to the engine. Can keep aptitude. In addition, it is possible to adjust the heat transfer by adjusting the contact area between the step portion and the step contact portion.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a pressure sensor plug of the present invention will be described with reference to the drawings based on first and second embodiments in which a pressure sensor spark plug is applied. [Structure of First Embodiment] FIGS. 1 to 6 are for explaining the first embodiment. FIG. 1 is a sectional view of a spark plug with a pressure sensor mounted on a cylinder head of an engine, and FIG. 1 is a top view, FIG. 3 is a sectional view of an essential part of the spark plug, and FIG. 4 is an exploded view of an essential part of the spark plug.

The pressure sensor-equipped spark plug is a combination of a spark plug 2 for performing a spark discharge in a combustion chamber 1 of an engine and an annular pressure sensor 3 mounted on the spark plug 2. The cylinder head 4 of the engine to which the spark plug 2 is assembled has a mounting recess 5 for mounting the spark plug 2 on the cylinder head 4.
At the bottom of the mounting recess 5, an insertion hole 6 for guiding the end of the spark plug 2 into the combustion chamber 1 is formed.
Are formed. The side wall of the mounting recess 5 is formed with a lead groove 5a for arranging an output lead wire 24, which will be described later. In addition, the spark plug 2 is defined in claim 1.
In the plug, the reference numeral 7 in the figure corresponds to the insertion portion to be inserted into the insertion hole 6. Further, the portion of the spark plug 2 other than the cap nut 15 described later corresponds to the main body portion (no reference numeral).

The spark plug 2 has a center electrode 12 that receives a high voltage through a terminal 11 provided at one end, a substantially cylindrical insulator 13 that insulates and holds the center electrode 12, and an insulator 13 that holds the insulator 13. In this state, the metal shell 14 is fixed to the cylinder head 4 of the engine, and the tubular cap nut 15 that fixes the spark plug 2 to the engine by pressing the metal shell 14 against the cylinder head 4 of the engine. It The center electrode 12 and the insulator 13 shown in this embodiment are well known.

The metal shell 14 has an insulator 13 inside.
It is a substantially tubular metal member that firmly holds the insertion tube 16, and includes an insertion tube 16 inserted into the insertion hole 6 and a seat portion 17 having a diameter larger than that of the insertion tube 16. The insertion tube 16 is a tube body having no thread formed on the periphery thereof, and an outer electrode 18 arranged opposite to the center electrode 12 is fixed to the end portion by welding or the like. Seat 17
Is urged toward the bottom of the mounting recess 5 by the cap nut 15. Between the seat 17 and the bottom of the mounting recess 5, a gasket 19 for preventing the outflow of combustion gas and an annular pressure are provided. The sensor 3 is pressed in the axial direction. In this way, the seat portion 17 corresponds to a pressing portion that presses the pressure sensor 3 in the axial direction.

The cap nut 15 is a tubular metal fitting provided separately from the metal shell 14 and is provided separately from the main body. Around the cap nut 15, a male screw 22 that can be screwed into a female screw 21 formed on the inner periphery of the mounting recess 5 is formed. Also, around the upper side of the cap nut 15 in the figure,
The hexagonal bolt portion 23 is formed, and by screwing the cap nut 15 with a fastening tool (not shown),
The seat portion 17 of the metal shell 14 is urged toward the bottom of the mounting recess 5 to fix the spark plug 2 to the cylinder head 4, and the gasket 19 and the pressure sensor 3 are attached to the seat portion 17.
It is firmly sandwiched between and the bottom of the mounting recess 5.

The pressure sensor 3 is a ring-shaped sensor having a well-known structure using a piezoelectric element or the like, and generates an output signal according to a change in pressure applied in the axial direction. The output signal generated by the pressure sensor 3 is output to the output lead wire 24.
Is transmitted to a detection circuit (not shown) via.

[Operation of Embodiment] Next, the operation of measuring the pressure in the combustion chamber 1 by the spark plug with a pressure sensor will be described. The engine equipped with the spark plug with the pressure sensor is a well-known gasoline engine, and when the compressed air-fuel mixture supplied into the combustion chamber 1 is ignited, the pressure in the combustion chamber 1 rapidly rises due to combustion (explosion). . Then, the increased pressure falls due to the explosion stroke and the exhaust stroke due to the explosion.

The increase in pressure caused by the explosion of the compressed air-fuel mixture is also given to the spark plug 2 exposed in the combustion chamber 1. The metal shell 14 for fixing the spark plug 2 to the cylinder head 4 receives the pressure rising energy applied to the spark plug 2, and as a result, the pressure rising energy becomes energy for the seat portion 17 to rise. Thus, when the rising energy is applied to the seat portion 17, the axial force applied to the pressure sensor 3 changes, and the pressure sensor 3 outputs a signal corresponding to the change in the axial force.

[Experimental Results] Next, experimental results are shown in which the spark plug with the pressure sensor of the present embodiment and the spark plug with the pressure sensor of the conventional structure (see FIG. 8) are compared. FIG.
Shows the variation of the output signal of the pressure sensor 3 caused by the attachment / detachment of the pressure sensor-equipped spark plug. The solid line shows the measurement result of the pressure sensor-equipped spark plug of this embodiment, and the broken line shows the pressure sensor-equipped spark plug of the conventional structure. The measurement result of is shown.

As can be seen from FIG. 5, in the spark plug with a pressure sensor of this embodiment, the pressure sensor 3 generates a high output signal and the output value has a very small variation. On the other hand, in the spark plug with a pressure sensor having the conventional structure, the output signal of the pressure sensor is low and the variation in the output value is extremely large.

FIG. 6 shows the hysteresis of the output signal due to the pressure increase and the pressure decrease of the pressure sensor 3, the solid line shows the measurement result of the spark plug with the pressure sensor of this embodiment, and the broken line shows the spark plug with the pressure sensor of the conventional structure. The measurement result of is shown. As can be seen from FIG. 6, the pressure sensor 3 including the spark plug with the pressure sensor of the present embodiment has extremely small hysteresis. On the other hand, the pressure sensor using the spark plug with the pressure sensor having the conventional structure has a large hysteresis.

[Effect of the First Embodiment] In the spark plug with the pressure sensor of the present embodiment, the high pressure combustion gas generated by the explosion of the compressed air-fuel mixture in the combustion chamber 1 has a small screw fitting portion as in the conventional case. Does not flow into the gap. Therefore, unlike the conventional technique, the pressure sensor 3 does not receive the influence of the combustion gas flowing into the minute gap of the screw fitting portion and the influence of the gas gradually flowing out from the minute gap, and the pressure change in the combustion chamber 1 does not occur. Can be directly received by the pressure sensor 3.
As a result, as shown in FIG. 6, the hysteresis of the output signal of the pressure sensor 3 can be suppressed smaller than that in the conventional case.

In the prior art, the energy generated by the explosion of the compressed air-fuel mixture in the combustion chamber 1 is
Before reaching 7, the energy was partially absorbed by the screw fitting portion in the insertion hole 6, but in the present embodiment, the boosting energy is not absorbed in the insertion hole 6 and the seating force is directly absorbed. Reported to section 17. As a result, as shown in FIG. 5, the output of the pressure sensor 3 is higher than in the conventional case, and the detection accuracy in the combustion chamber 1 can be improved.

[Second Embodiment] FIG. 7 shows a second embodiment and is a cross-sectional view of a spark plug with a pressure sensor mounted on a cylinder head 4 of an engine. The cylinder head 4 of the engine of this embodiment includes an annular step portion 31 for reducing the inner diameter of the insertion hole 6 on the combustion chamber 1 side. The step portion 31 is formed in a tapered shape whose diameter is narrowed toward the combustion chamber 1. Further, the insertion tube 16 of the metal shell 14 (the portion that is inserted into the insertion hole 6) has a step portion 31.
An annular step abutting portion 32 that comes into contact with is formed. The step contact portion 32 is also formed in a tapered shape so as to match the tapered shape of the step portion 31.

In the second embodiment, the heat transferred from the insulator 13 to the metal shell 14 is provided with the contact portion between the step portion 31 and the step contact portion 32, so that the metal shell 14 and the cylinder head 4 are provided. As a result, the contact area with the metal shell becomes large, and as a result, the heat transferred from the insulator 13 to the metal shell 14 is efficiently transferred to the cylinder head 4. In this way, by adjusting the contact area between the step portion 31 and the step contact portion 32, the temperature of the insulator 13 can be maintained at an appropriate temperature, and as a result, the heat dissipation of the spark plug 2 can be brought to an appropriate value. Can be set.

[Modification] In the above embodiment, the spark plug 2 is shown as an example of the plug, but other plugs such as a glow plug which are externally mounted in the insertion hole 6 communicating with the combustion chamber 1. The present invention may be applied to. Further, the plug is directly attached to the bottomed hole of the cylinder body of the engine, and may be in the form of a rod-shaped main body having no screw and a pressing portion for pressing the pressure sensor in the axial direction. Although the example in which the cap nut 15 is provided separately from the metal shell 14 is shown, the cap nut 15 and the metal shell 14 may be integrally provided by using a welding technique. The output signal of the pressure sensor 3 may be used as a knock sensor or a combustion pressure detecting sensor.

[Brief description of drawings]

FIG. 1 is a sectional view of a spark plug with a pressure sensor mounted on a cylinder head of an engine (first embodiment).

FIG. 2 is a top view of FIG. 1 (first embodiment).

FIG. 3 is a sectional view of a main part of a spark plug (first embodiment).

FIG. 4 is a perspective view of a main part of the spark plug (first embodiment).

FIG. 5 is a graph showing variations in the output signal of the pressure sensor caused by desorption (first example).

FIG. 6 is a graph showing the hysteresis of the output signal of the pressure sensor (first embodiment).

FIG. 7 is a cross-sectional view of a spark plug with a pressure sensor mounted on a cylinder head of an engine (second embodiment).

FIG. 8 is a sectional view of a main part of a spark plug with a pressure sensor mounted on a cylinder head of an engine (prior art).

[Explanation of symbols]

 1 Combustion Chamber 2 Spark Plug 3 Pressure Sensor 4 Cylinder Head (Part of Engine) 6 Insertion Hole 7 Insertion Part 12 Center Electrode 13 Insulator 14 Metal Fitting 15 Cap Nut 16 Insertion Cylinder (One of Metal Fittings Inserted in Insertion Hole Part) 17 seat part (corresponding to pressing part) 31 step part 32 step contact part

Claims (3)

[Claims] 1. A plug that includes an insertion portion that is inserted into an insertion hole that communicates with a combustion chamber of an engine, and that has a pressing portion that is pressed toward the engine; and a plug that is disposed between the engine and the pressing portion. In the plug with a pressure sensor including a pressure sensor, the plug is provided so as to be screwed to the main body portion having the pressing portion and the engine, and is screwed into the engine, whereby the main body portion is A plug with a pressure sensor, comprising a cylindrical cap nut that is fixed to the engine and that presses the pressure sensor between the pressing portion and the engine. 2. A plug with a pressure sensor according to claim 1, wherein the plug is a spark plug for igniting the inside of the combustion chamber, a center electrode to which a high voltage is applied, an insulator for insulating and holding the center electrode, A metal shell fixed to the engine while holding an insulator is provided, wherein the metal shell is inserted into the insertion hole.
A screw to be screwed into the engine is not formed, and the metal shell is fixed to the engine by the cap nut, so that the metal shell, the insulator, the center electrode, and the seat portion of the metal shell are attached. The intervening pressure sensor
A plug with a pressure sensor, which is fixed to the engine. 3. The plug with a pressure sensor according to claim 2, wherein the engine in which the insertion hole is formed is provided with an annular step portion for reducing an inner diameter of the insertion hole on the combustion chamber side, and A plug with a pressure sensor, wherein an annular step abutting portion that abuts the step is formed in a portion of the metal shell that is inserted into the insertion hole.